1. Technical Field
The present invention relates to a polishing apparatus for a semiconductor wafer and, more particularly, to a platen structure of the polishing apparatus, and to a method for exchanging a polishing pad affixed to the same. This can allow the polishing pad for planarizing a metallic layer formed on the wafer surface to be exchanged for a new pad without interrupting the operation of the equipment in the manufacturing process of semiconductor devices.
2. Discussion of Related Art
Generally, semiconductor devices have a step whose height is increased with high densification, scale-down in line width, and multi layered metallization. In order to planarize this step, various planarizing methods such as spin on glass (SOG), etchback, reflow and the like have been developed and employed.
As for such planarizing process for wafers, there are two methods comprising a mechanical polishing method and a chemical polishing method. The mechanical polishing has a drawback of forming a strained layer in the wafer during polishing. Although such strained layer is not formed, the chemical polishing also has a drawback in that it is difficult to form a planarized shape on the wafer. Thus, obtaining shape precision is not easy to accomplish. A planarizing process has been developed combining mechanical and chemical polishing, i.e., a chemical mechanical polishing (CMP) technology. The CMP process is implemented by rotating a polishing table on which a polishing pad is attached. This is done while pressing a polishing head being rotated and vibrated at a time, with a certain pressure exerted towards the polishing table. The polishing head is attached by means of surface tension or vacuum. Then, the wafer surface contacts the polishing pad using the weight of the polishing head itself and pressure applied from an exterior source. A slurry of polishing solution flows through a fine gap between the contact surfaces to facilitate a mechanical removal operation by grinding particles contained in the slurry and surface protrusions of the polishing pad, and a chemical removal operation by chemical components of the slurry.
Such a polishing apparatus is disclosed in U.S. Pat. No. 6,520,895 B2. The polishing apparatus of U.S. Pat. No. 6,520,895 B2 includes a wafer chuck for supporting a wafer while directing the wafer surface to be polished upwards, a polishing pad for polishing the surface to be polished, and a polishing head for supporting the polishing pad while directing the grinding surface of the pad downwards. In this polishing apparatus, a vacuum suction device is provided at a lower portion of the polishing head so as to detachably and fixedly support the polishing pad such that the grinding surface of the pad faces downwards, by which the vacuum suction device and the polishing pad supported by the polishing head can be automatically exchanged.
The conventional polishing apparatus of FIGS. 1, 2a and 2b, respectively, includes a polishing head 10 for vacuuming a wafer 12, a polishing pad 16 mounted below the polishing head 10 so as to polish the wafer 12, a platen 20 for fixing the polishing pad 16, a pad conditioner 14 mounted spaced in horizontal direction located apart at a certain distance from the polishing head 10 so as to maintain the surface state of the polishing pad 16 constant, a cleaning cup 18 for cleaning the pad conditioner 14, and a head cup load unit (HCLU) 22 for loading the wafer 12 to the polishing head 10.
The wafer 12 loaded from the HCLU 22 is moved by vacuum onto the polishing head 10, and the polishing head 10 retaining the wafer 12 moves the wafer 12 toward each platen 20. After the movement, the polishing head 10 exerts a pressure toward the platen, thus to the wafer positioned between the polishing pad 16 of the platen 20 and the polishing head 10. Then, the polishing pad 16 and the polishing head 10 are rotated to polish a portion of the wafer. Herein, at a certain cycle during the continuous polishing of the wafer, a controller (not shown) controls the polishing head 10 to be positioned spaced apart from the polishing pad 16 and operates the driving of the CMP equipment including interrupting the supply of the slurry through the nozzle.
Further, the pad conditioner 14 plays an important role in the polishing operation, as follows:
First, the pad conditioner 14 sweeps the polishing pad so that the slurry of polishing solution is distributed uniformly around the whole surface of the wafer, which prevents the wafer from being locally polished. Second, if the polishing pad 16 contacts and continuously polishes the wafer 12, a groove of the polishing pad 16 is worn out due to friction therebetween and thereby degrading the performance of the polishing. The pad conditioner 14 exerts at its diamond disc a force against the polishing pad 16 so that the roughness of the polishing pad can be maintained at a certain level through the sweeping and rotation of the pad conditioner, which prevents the degradation in performance of polishing.
The operation of exchanging the polishing pad 16 supported by the platen 20 will now be described in the conventional wafer polishing apparatus, such as in the above apparatus. The wafer polishing apparatus including platens 20 is interrupted in its operation when all of the platens 20 are idled. Upon the exchange of the polishing pad 16, the polishing head 10 is moved or detached to provide a space for the pad exchange. Then, the used polishing pad 16 is removed and a new polishing pad 16 is attached to the platen 20. Finally, the polishing head 10 that has been moved or detached for securing the exchange space is returned to its original position.
However, the platen structure of the conventional wafer polishing apparatus constructed as above has a problem in that the exchange of the polishing pad is inconvenient and time-consumable to implement. This is because the exchange of the polishing pad supported by the platen is conducted by interrupting the operation of equipment, moving or detaching the polishing head for securing a space for exchange, and finally exchanging the polishing pad.